1. Field of the Invention
The present invention relates to a solid-state imaging device for removing a background light component of light incident on a photodetector and detecting only a signal light component.
2. Related Background Art
A solid-state imaging device has a plurality of photodetectors in a one- or two-dimensional array, in which a signal current output from each photodetector is integrated by an integration circuit, and a signal voltage as an integration result is output. Some solid-state imaging devices convert (A/D-convert) the signal voltage as an analog signal into a digital signal and output the digital signal. If the signal voltage exceeds a predetermined value in this A/D conversion, the digital signal that is A/D-converted and output on the basis of the signal voltage is saturated at a value corresponding to the predetermined value, and consequently, accurate photodetection cannot be performed. Conventionally, the expected maximum value of the signal voltage or a value more than the expected maximum value is set as the predetermined value, thereby preventing the saturation. Alternatively, the dynamic range is widened using a technique such as logarithmic compression.
A solid-state imaging device is used for a distance measuring device installed in, e.g., a camera. In this distance measuring device, reflected light of spot light projected from a light projecting means such as a light-emitting diode to an object is sensed by each of two solid-state imaging devices, and distance measurement is executed on the basis of the two sensed images. In sensing a spot light component (signal light component), a background light component is also superposed and sensed. Hence, only the background light component is sensed by each of the two solid-state imaging devices when no spot light is projected, and the difference between the two images is calculated to obtain the image of only the spot light component, thereby improving the distance measuring accuracy.